The agency scooped the account, believed to be worth six figures, following a competitive pitch.
Paratus will now handle all English regional comms for the scheme, which offers grassroots community groups and voluntary organisations awards of £300 to £10,000.
The agency will use case studies of successful applicants to ensure that potential applicants are aware of their eligibility for grants. It will target regional papers, broadcast and online media.
Paratus co-founder John Rivett will head up the account, reporting to the Big Lottery Fund's director of comms and marketing Linda Quinn.
The Big Lottery Fund is the largest of the National Lottery good cause distributors. Government raids on the fund to pay for the 2012 Olympics have provoked widespread anger from the third sector, as groups fear huge funding cuts.
The organisation had to provide £213.1m for the Olympics in 2003, and a further £425m in March last year. At the end of last year it emerged that special Lottery games would hit funding further, with an estimated loss of £287.5m.
Other Paratus voluntary sector clients include communications charity I Can and The Drinkaware Trust.